1. Field of the Invention
This invention relates generally to vehicle steering devices, and more particularly, this invention relates to vehicle steering devices for controlling torque.
2. Description of the Related Art
In a motor vehicle, a pull condition can occur in which a driver of the vehicle has to input torque into the steering system in order to maintain a straight path. This condition can be caused by vehicle and road conditions and weather conditions such as a crosswind that require a force for the steering system to overcome, or by an imbalance in the steering system (such as if the valve is balanced in the null position and the torsion bar is on center but the valve spool is creating pressure in the system) which requires an input torque by the driver to correct. Various designs are known for controlling input torque. One design includes the use of cogs in steering mechanisms.
Cogging torque has significant influence on the output torque profile of torque overlay (TO) actuators. For example, due to interactions of a permanent magnet with teeth of a cog, cogging or detent torque is caused. Cogging torque can be minimized using conventional methods, such as by providing skew (in at least one of the permanent magnet and teeth of the cog), a dummy notch in each of the teeth or selected teeth, and by shifting of the permanent magnet or teeth. For a permanent magnet having a ring design, including skew is a simple design around.
What are needed are advancements in techniques for controlling cogging torque in a steering mechanism.